Remove event caching code

Flushing the events cache worked by updating a recent number of rows in
the "events" table. This has the result that on PostgreSQL a lot of dead
tuples are produced on a regular basis. This in turn means that
PostgreSQL will spend considerable amounts of time vacuuming this table.
This in turn can lead to an increase of database load.

For GitLab.com we measured the impact of not using events caching and
found no measurable increase in response timings. Meanwhile not flushing
the events cache lead to the "events" table having no more dead tuples
as now rows are only inserted into this table.

As a result of this we are hereby removing events caching as it does not
appear to help and only increases database load.

For more information see the following comment:
https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/6578#note_18864037

1 files changed, 0 insertions, 12 deletions

diff --git a/app/models/merge_request.rb b/app/models/merge_request.rb
index 6c3c093d084..bf9edb0b823 100644
--- a/app/models/merge_request.rb
+++ b/app/models/merge_request.rb
@@ -601,18 +601,6 @@ class MergeRequest < ActiveRecord::Base
     self.target_project.repository.branch_names.include?(self.target_branch)
   end
 
-  # Reset merge request events cache
-  #
-  # Since we do cache @event we need to reset cache in special cases:
-  # * when a merge request is updated
-  # Events cache stored like  events/23-20130109142513.
-  # The cache key includes updated_at timestamp.
-  # Thus it will automatically generate a new fragment
-  # when the event is updated because the key changes.
-  def reset_events_cache
-    Event.reset_event_cache_for(self)
-  end
-
   def merge_commit_message
     message = "Merge branch '#{source_branch}' into '#{target_branch}'\n\n"
     message << "#{title}\n\n"